"Normal" microflora can cause serious infections in cancer patients and preventive measures by which these infections can be eliminated are essential. The objective of this study is to evaluate the effectiveness of new antimicrobial agents against such microflora. Enterobacteria and S. aureus were susceptible to netilmicin, tobramycin, gentamicin, and amikacin. Susceptibility of P. aeruginosa was variable. S. faecalis was susceptible to netilmicin and resistant to amikacin. Both ticarcillin (T) and carbenicillin (C) were effective against gram positive bacteria, E. coli, and P. mirabilis, but T was the more active against P. aeruginosa than C. Piperacillin, azlocillin, and mezlocillin were more active than C and T against most genera. Daunorubicin and cytosine arabinoside exerted an antagonistic effect on the activity of the aminoglycosides mentioned above, but not against kanamycin. Two new cytotoxic agents, Peptichemio and Ledacrine, had no antifungal activity, but miconazole (M) and miconazole nitrate (MN) were inhibitory against C. albicans and the majority of T. glabrata strains. Rifampin frequently enhanced this inhibition. The antifungal R41400 did not effect most T. glabrata and Candida spp. other than C. albicans.